The present invention relates to rotary connectors, and more particularly, to an improved spring-loaded rotary connector using spring loaded rotating ball contacts.
In prior ball-based spring-loaded rotary connectors developed by the assignee of the present invention, the connectors have only provided zero-, one- or two-degree-of-freedom motion, which results in relatively large wear-out of certain components of the connectors. This causes a loss of the contact between the contacts of the connector and a flat flexible printed wiring board to which the contacts mates.
For a connector with a bump- or dimple-type contact located between two flat flexible printed circuits, such as is disclosed in U.S. Pat. No. 5,484,294, entitled "Brushless Rotary Connector", for example, which patent is assigned to the assignee of the present invention, relatively tight tolerances in the distance between two flat flexible printed circuits and in the size of the bumps or dimples are required. For a connector with one-degree-of-freedom motion along an axial direction of its contacts, such as is disclosed in U.S. patent application Ser. No. 08/724,591, filed Sep. 30, 1996, entitled "Spring Loaded Contact Device and Rotary Connector", for example, also assigned to the assignee of the present invention, the connector uses spring-loaded plungers having round shaped heads.
It has been found that misalignment (tilt angle) and variation in the compression distance for each plunger, which causes the change in the spring restoring force applied in the plunger, occur during the installation process for the connector disclosed in the above-cited patent application. These two conditions can result in relatively large variations in the friction forces exerted in the connector during operation because the contacts are not free to move in directions perpendicular to the axis of the plunger.
For a connector having two-degree-of-freedom motion in directions parallel to the surface of the flat flexible printed circuits (such as in connectors using bearing balls), the relatively tight tolerances in the distance between two flat flexible printed circuits and in the size of the bearing balls are required. U.S. Pat. No. 5,575,664 issued Nov. 19, 1996 entitled "Ball Contact Rotary Connector", assigned to the assignee of the present invention describes this type of connector. In addition, to ensure full contact between the connectors and the flat flexible printed circuits in a vibration environment, an adequate spring load applied in the plunger or smaller tolerance for the connectors with bump-, dimple- or ball-bearing-type is required. The more severe in vibration environment, the higher spring load or smaller tolerance is necessary, which results in higher friction force applied in the plunger's tip or connectors.
Therefore, it is an objective of the present invention to provide for an improved spring-loaded rotary connector using spring-loaded rotating ball contacts.